Smoking is a major cause of heart disease for both men and women. Measuring urinary nicotine metabolite cotinine is a popular and established method of biologically monitoring exposure to tobacco smoke. Lipid profile, blood pressure, cardiac-specific troponins, etc. have been successfully used as biomarkers to help diagnose, evaluate and monitor individuals suspected of having heart problems or carrying the risk of atherosclerosis. However, the development of a single biological important and clinically validated biomarker remains an unmet challenge for measuring exposure to tobacco smoke and for assessing cardiac function at the same time. MicroRNAs (miRNAs) are short 20-25 nucleotide RNA molecules that negatively regulate gene expression. Over 1,000 human miRNA genes have been identified. Recently, altered miRNA expression has been reported in various tobacco-related diseases such as cardiovascular dysfunction, and the profiles of tissue miRNAs exhibit great potential for diagnostic applications. Moreover, miRNAs are remarkably stable in human plasma or serum. Differential levels of circulating miRNAs have been associated with ischemic heart disease, heart failure, and coronary artery disease. However, there are limited studies on circulating miRNAs upon tobacco exposure. Our hypothesis is that miRNAs can serve as blood-based biomarkers for linking tobacco exposure to heart disease. In this proposal, we propose one specific aim to determine whether there is a signature of circulating miRNAs that can link tobacco smoke to heart disease. We will first profile miRNAs differentially present in the plasma in four groups of human subjects: smokers with or without heart disease and non-smokers with or without heart disease using miRNA deep-sequencing and quantitative real-time PCR. We will then examine the circulating miRNA changes in smokers with or without myocardial infarction who are asked to quit smoking. We will also profile circulating miRNAs in mice following exposure to acute or chronic tobacco smoke with or without induced myocardial infarction. Finally, we will analyze the miRNA alterations in both humans and mice, compare them to reported circulating miRNA profiles in various human cardiovascular pathologies, and formulate a miRNA signature that can be used as biomarkers to associate heart disease with tobacco exposure. Data generated from this research will directly assess biologically relevant changes associated with tobacco use in both humans and mice and will contribute to the science base to inform the FDA's regulation of tobacco products.